1. Field of the Invention
The present invention relates to an oil heating apparatus for an internal combustion engine and, more particularly, to an oil heating apparatus for improving a low-temperature starting property of an internal combustion engine.
2. Description of the Related Art
An internal combustion engine, e.g., a diesel engine, is not easily started at low temperatures, mainly because of a decrease in ignitability of a fuel-gas mixture compressed inside a cylinder, and because of an increase in viscosity of a lubricating oil due to the low temperatures, which increases the load on an oil pump and the rotation resistance of the engine.
Conventionally, the compression ignitability of the fuel-gas mixture at low temperatures can be improved by only a negligible extent by a starting aid. For example, a glow device for preheating the fuel-gas mixture or a device for changing the fuel ignition timing upon starting may be additionally provided to a diesel engine main body. The problem of the resistance due to high viscosity of an oil at low temperatures, on the other hand, is solved by improving the characteristic of the lubricating oil itself or by selectively using the lubricating oil in accordance with seasons or districts.
Not only in the diesel engine but also in a gasoline engine, an engine starting property during a cold period depends on the compression pressure, i.e., a cranking speed. The higher the cranking speed, the easier the engine is to start and the lower the load on a battery. When the engine is started under cold conditions, since the viscosity of an engine oil is increased, the driving force for an oil pump cannot be ignored. For example, when the outdoor temperature is -25.degree. C., about 10% of a starter output is consumed in order to drive the oil pump. Therefore, the cranking speed is limited, and the starting property is degraded. Conversely, a starting aid for controlling the viscosity of an oil to a low value is not available.
Lubricating oils having a low viscosity at low temperatures are usually expensive, and some oils have an adverse influence upon the engine main body during normal engine operation. Further, it is cumbersome and incurs a high running cost to select and replace an optimal oil in accordance with seasons and districts.